Screen assemblies are used in the aggregate business for separating rock, crushed rock, gravel, sand, and the like (referred herein as material) into various sizes. Screen assemblies typically comprise one or more screen decks containing a perforated screening medium, which acts as a sieve through which the material is separated. A charge of material is deposited on the receiving end of the screen deck of a screen assembly, and as the material is conveyed to the discharge end, smaller material falls through the openings leaving the larger material retained on the screen deck. In a three-deck screen assembly, for example, larger material is retained on the upper screen deck and conveyed off of the screen deck at the upper discharge end, the medium-sized material is retained on the middle screen deck and conveyed off of the screen deck at the middle discharge end, the smaller size material is retained on the lower screen deck and conveyed off of the screen deck at the lower discharge end, and the smallest material is deposited below the lower screen deck.
Screen assemblies generally come in two basic screen deck configurations; inclined and horizontal, both of which use vibratory motion to help pass the material through the screening medium as the material is conveyed across the screen decks. Inclined screen assemblies have one or more screen decks with an elevated receiving end. The movement of material across the screen deck is provided by gravity in combination with the assistance of a vibrating mechanism. Horizontal screen assemblies convey material across the deck by virtue of the vibration of the screen assembly being angularly directed from the receiving end to the discharge end and by mounting the screen assembly on springs.
The screen deck generally consists of a rigid frame upon which a screening medium is laid or supported. The screening medium contains a plurality of openings of a predetermined size. Examples of screening medium include woven wire cloth, perforated plate and urethane plates with presized holes. When multiple screen decks are used, they are held together by large side plates, thereby making a screen assembly or a basket. To withstand the wear and tear of material separation process, screen assemblies are constructed out of heavy-duty steel, resulting in the screen assemblies weighing several tons.
It has been found that in certain screening applications, the screen assemblies have been prematurely failing when run at higher operating speeds, such as those desired when separating finer materials or in wet screening applications. In particular, the bracing of the screen decks, as well as the side plates and connections prematurely crack, leading to failure of the screen assemblies. These failures have occurred even where the screen assembly has substantial useful life remaining.
There is a need for an improved screen assembly design that will prevent screen assembly failure, e.g. cracking of the screen decks, side plates and the like, especially where the charge loads are greater thus resulting in a greater overall operating weight, or when a higher operating speed is required for effective separation.